英文:
Unique email in Google Datastore
问题
我有一个包含Email字段的User实体。User实体的ID是一个ULID，因为我想允许用户更改他们的电子邮件地址，但我希望确保电子邮件地址在CREATE和UPDATE时都是唯一的。
我正在使用Datastore事务。这是一个代码片段：
ctx := context.Background()
k := datastore.NameKey("User", user.ID, nil)
_, err := client.RunInTransaction(ctx, func(t *datastore.Transaction) error {
// 其他需要在事务中的操作
_, err = t.Put(k, user)
return err
})
return err
Email字段已经建立了索引。有没有办法在事务中搜索当前用户的电子邮件地址？
*datastore.Transaction没有GetAll方法，所以我无法像这样运行查询：
datastore.NewQuery("User").Filter("Email =", user.Email)
我担心使用
client.GetAll(ctx, q, nil)
不能保证在事务中的隔离性。
英文:
I have a User entity containing an Email field. The User entity id is a ULID, because I want to allow users to change their email addresses, but I want to ensure that the email address is unique on both a CREATE and an UPDATE.
I am using Datastore transactions. This is a code fragment:
ctx := context.Background()
k := datastore.NameKey("User", user.ID, nil)
_, err := client.RunInTransaction(ctx, func(t *datastore.Transaction) error {
// other stuff that needs to be in transaction
_, err = t.Put(k, user)
return err
})
return err
The Email field is indexed. Is there any way to search the User entity for the current user's email address as part of the transaction?
*datastore.Transaction does not have a GetAll method, so I cannot run a query like this:
datastore.NewQuery("User").Filter("Email =", user.Email)
I'm afraid that using
client.GetAll(ctx, q, nil)
will not guarantee isolation within the transaction.
答案1
得分: 4
简短的回答是不可以，除非你查询的是特定的实体组，否则不能将查询作为事务的一部分。全局查询始终是最终一致的。然而，将所有内容放在一个单一的实体组中可能会严重限制写入吞吐量。
一种解决方法是创建另一个种类（Kind），其中的实体将电子邮件地址映射到用户。然后，在一个事务中，你可以检查电子邮件实体，如果它不存在或指向错误的位置，可以将电子邮件实体和用户实体一起设置为一个事务。
英文:
The short answer is no, you cannot use a query as part of a transaction unless you are querying a specific entity group. Global queries are alway eventually consistent. However, to put everything in a single entity group would likely limit write throughput too much.
A workaround is you can have another Kind with entities that map email addresses to users. Then you can, in a transaction, check the email Entity and if it doesn't exist or it points to a bad location, set the email Entity and the user Entity all as a single transaction.
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